I had my cervical spine fused at the C45 level about two years ago. I remember being told that it might cause the level above or below to go bad in time. So far, nothing has happened. How long does it take before this starts to happen?

Adjacent segment disease (ASD) may be a long-term consequence of spinal fusion. But it may just be what happens over time as a result of aging and degenerative changes. The argument centered on the cause(s) of ASD hasn't been settled yet. There's enough evidence to suggest it's the result of many factors (multifactorial).

X-ray findings showing degeneration at the level next to a spinal fusion reportedly occur in 25 to 92 per cent of all cases. Analysis of data collected so far suggests at least a 25 per cent rate of ASD by the end of 10 years. That means one in four patients develops ASD after spinal fusion.

But that also means not everyone develops significant or symptomatic ASD. You may develop some degenerative changes that never cause you any problems. And reoperation rates for ASD are fairly low at this time. For those who do develop ASD, it doesn't become evident until around seven to eight years after the first operation.